Turbine engines currently utilize either a variable continuous stream or a pulsed stream to provide fuel to the engine. The primary objectives of both of these methods are to control the amount of fuel delivered to the engine and to attempt to deliver said fuel in the smallest droplet size, equally dispersed throughout the combustion area to promote rapid and complete combustion of the fuel. The continuous stream method relies upon control of the quantity of fuel delivered to the engine at some arbitrary point upstream of fuel utilization and by mechanical fractionation of the fuel stream while the pulsating injection method as taught by Nearhoof, et. al. in U.S. Pat. No. 6,742,430 (“Fuel Injection Control System for a Turbine Engine”) rapidly turns the fuel on and off at the point of usage to achieve fractionation and control of the combustion process.
The continuous stream method suffers the problems of complexity of the metering equipment, limitations on the final fuel particle size due to utilizing mechanical breakup/dispersion techniques, and slow system response to changing loads due to the mechanical equipment comprising the fuel system. A further limitation of the continuous stream method is in the inherent weight and precision manufacturing tolerances of the necessary metering pump(s) and/or valve(s) to control fuel flow.
The pulsating injection method overcomes the limitations of the continuous stream method by eliminating the precision mechanical controls and the need for mechanical fractionation of the fuel stream but the engine is subject to loss of flame stability at low pulse on-times due to the proportionally long time when no fuel is being supplied during each pulse cycle.
This invention is designed to overcome these limitations by elimination of the mechanical metering equipment such as pumps and valves and by controlling groups of injectors independently rather than pulsing all injectors at the same time. Controlling groups of injectors overcomes the flame stability associated with pulsing all injectors at the same time along with maintaining the response and simplicity of the fuel delivery system lacking in the continuous stream method. The problem of flame stability has previously been overcome by introducing a small quantity of fuel through a continuously fed injector during periods when the main injectors are operating at a low duty cycle or by cycling the main injectors at a relatively high frequency to keep the off-time of each pulse short enough to maintain the combustion process over the more stable continuous stream delivery system. By sequentially operating groups of injectors, the time that the engine's fuel supply is shut off is reduced which allows the frequency of injector pulsing to be reduced to improve upon the overall life of the injectors and elimination of the supplemental continuous injector relied upon to maintain the combustion process.